Provided is improved technology for vehicle speed estimation. Vehicle speeds are estimated using visual information derived from a camera, for example in an LPR system. Calibration is provided to allow the system to estimate vehicle speeds in a variety of setups including setups where the images are provided from cameras that are located off-center from a traffic lane, for example on the side of the road. Calibration may be done with as little as a single passage of an unknown vehicle. In some embodiments it may be done alongside speed estimation with every vehicle detected/estimated.
In accordance with a non-limiting example is provided a method for calibrating a vehicle speed estimation system that employs a camera having a set of camera parameters to estimate the speed of vehicles based on images received from the camera, the images defined in an image space and the vehicles and camera each belonging to a physical space and having an absolute position therein. The method comprises receiving at a controller from the camera a calibration image stream comprising a first image of a vehicle captured at a first time and a second image of the vehicle captured at a second time, the first and second images having the same image space. The method further comprises at a controller executing controller logic to identify in each of the first and second image a vehicle feature having a known dimension in the physical space, the identifying comprising determining a placement of the vehicle feature in the image space at each of the first and second times. The method further comprises at the controller executing controller logic to define on the basis of the placement of the vehicle feature in the image space at each of the first and second times an absolute-position-independent relationship between an image space placement and a physical space position relative to the camera. The method further comprises at the controller, using controller logic, applying the absolute-position-independent relationship between an image space placement and a physical space position relative to the camera in a speed estimation algorithm to determine the speed of a vehicle captured by the camera.
In accordance with another non-limiting example is provided a camera-based visual speed estimation system for estimating the speed of vehicles on the basis of video output from of a camera. The camera-based visual speed estimation system comprises a controller camera input for receiving from the video output of the camera comprising at least first and second images of a travelling vehicle captured at respective first and second times, the first and second images being defined in an image space and the travelling vehicle and camera each belonging to a physical space and having respective absolute positions therein. The camera-based visual speed estimation system further comprises a tangible controller in communication with the camera input and receiving therefrom the video data from the camera comprising at least the first and second images. The controller comprises calibration logic executable on the controller for causing the controller to identify in each of the first and second image a vehicle feature having a known dimension in the physical space, the identifying comprising determining a placement of the vehicle feature in the image space at each of the first and second times. The controller further comprises calibration logic executable on the controller for causing the controller to define on the basis of the placement of the vehicle feature in the image space at each of the first and second times an absolute-position-independent relationship between an image space placement and a physical space position relative to the camera. The controller further comprises calibration logic executable on the controller for causing the controller to apply the absolute-position-independent relationship between an image space placement and a physical space position relative to the camera in a speed estimation algorithm to derive speed estimation data indicative of the speed of a vehicle captured by the camera. The camera-based visual speed estimation system further comprises a controller output in communication with the controller for receiving from the controller the speed estimation data and outputting the speed estimation.